Leetcode 7. Reverse Integer（水）

7. Reverse Integer

Easy

Given a 32-bit signed integer, reverse digits of an integer.

Example 1:

Input: 123
Output: 321

Example 2:

Input: -123
Output: -321

Example 3:

Input: 120
Output: 21

Note:
Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−2³¹,  2³¹ − 1]. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

class Solution {
public:
    int reverse(int x) {
        int fl = 0;
        if(x >= pow(2,31) || x <= -pow(2,31)) return 0;
        if(x<=0){
            fl = 1;
            x = -x;
        }
        long long ans = 0;
        while(x>0){
            ans = ans * 10 + (x%10);
            if(ans >= pow(2,31)) return 0;
            x = x/10;
        }
        if(fl==1) ans = -ans;
        return ans;
    }
};